The present invention relates to an apparatus which equalizes, or at least reduces differences in tension, among a web comprising a multiplicity of strands, and more particularly to an apparatus designed to overfeed tighter strands in order to loosen those strands with an overfeed roll.
Many industry segments utilize multiple strands of elongated elements in various processes. In some processes, multiple strands are preferably fed at a substantially uniform tension to reduce or prevent unwanted effects. Various industries including the carpet industry, textile industry, tire cord industry, and others have processes where multiple strands are preferably fed at substantially the same tension. In fact, some problems can occur when particular strands in a web are at a significantly higher tension than others.
In the carpet industry, a tufting machine is generally utilized to tuft yarn into a backing to produce carpet having pile extending from a surface. The tufting machine generally has a multiplicity of needles, each fed with a strand of yarn. The yarn strands are typically fed to the tufting machine from a creel. When fed from a creel, some of the yarn strands are closer to the tufting machine than others. Other yarn strands travel through a more tortuous path than others. Accordingly, the resistance to movement is greater among some strands than others.
When yarn strands are fed to a tufting machine, those which have a higher resistance typically exhibit a higher tension than some others. Additionally, resistance may vary at different times on strands for many different reasons. When a higher tension yarn is run through the tufting machine, undesired effects could include the tufting of loops which are not the same height as those from xe2x80x9clooserxe2x80x9d yarn ends. If one were attempting to tuft a particular level over a section of carpet, the presence of a higher or a lower loop could be noticeable and cause the carpet product to be rejected. In cut pile carpets such an effect could require excessive tip shearing. Accordingly a need exists to equalize tension across multiple yarn ends.
The typical approach in the carpet industry has been to try to control tension in the individual strands which are slack, or exhibit a low tension. Many patents are believed to be directed to devices which apply tension to lower tension yarn strands. For instance U.S. Pat. No. 908,255 shows a braking system which increases tension on lower tension strands.
Other tension control devices utilize two successive wheels where yarn is completely wrapped around both wheels. U.S. Pat. No. 5,957,359 provides yarn to a first wheel which has a greater diameter than a second wheel, about which the yarns then pass. The first wheel xe2x80x9csupplies more length of fibre to the space between the wheelsxe2x80x9d than which passes over the second wheel (Col. 3, lines 23-35). Thus, all the tensions are raised at the first wheel, and then lowered between the first and second wheel due to the slightly slower speed of the second wheel. U.S. Pat. No. 4,087,956 appears to have somewhat similar double roll wrapped structure.
While many attempts have been made to equalize the tension, none are believed to be simple and effective. Accordingly, a need exists for an improved tension equalization device.
Consequently, it is an object of the present invention to provide a tension equalizing device for equalizing, or at least reducing the difference in tension, between multiple strands fed as a web.
It is a further object of the invention to utilize an overfeed roll to equalize tension by feeding tighter, or higher tension strands faster to thereby create slack in those strands.
It is another object of the invention to utilize gravity to assist with an overfeed roll to equalize tension across multiple strands.
Yet another object of the invention is to utilize an overfeed roll which contacts yarn along an arc of contact at the bottom half of the overfeed roll so that gravity and friction may assist in equalizing tension across a web.
Accordingly, an overfeed roll is positioned laterally to the direction of feeding of multiple strands. The strands contact the overfeed roll along a bottom portion of the circumference of the overfeed roll. Additionally, the arc which the strands contact the overfeed roll is preferably less than about two hundred and seventy degrees. As tighter strands are fed about the overfeed roll, the overfeed roll feeds these strands at a higher rate until they have similar slip characteristics as the looser strands. This is believed to be opposite of how almost every prior art device operates. Gravity may assist in pulling the strands away from the overfeed roll when the appropriate amount of slack is achieved in a high tension strand.